Effect of the Surface Polarity, Through Employing Nonpolar Spacer Groups, on the Glass-Transition Dynamics of Poly(phenyl methylsiloxane) Confined in Alumina Nanopores

Roksana Winkler,Karolina Adrjanowicz,Mateusz Dulski,Lukasz Laskowski,Wenkang Tu

doi:10.1021/acs.macromol.1c02145

Roksana Winkler, Karolina Adrjanowicz + Show 3 more

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https://doi.org/10.1021/acs.macromol.1c02145

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Abstract

Broadband dielectric spectroscopy and differential scanning calorimetry were used to study the effect of changes in the surface conditions on the segmental dynamics of poly(phenylmethylsiloxane) confined in alumina nanopores. Functionalization was done using highly polar propyl phosphoric units separated by the assumed concentration of triethoxysilane groups (from N = 0 to N = 24). By adjusting the proportion between polar units and nonpolar spacers, it was possible to control the surface polarity. Modification of the surface conditions does not inhibit the formation of the adsorbed layer, as revealed by the presence of two Tg’s in calorimetric results. However, changes in the surface polarity will prevent the growth of the additional interlayer in between the core volume and the interfacial layer. Finally, we also found that the changes in the surface polarity affect the equilibration kinetics and can be used to control the time scale of the structural recovery toward the equilibrium state.

Highlights

Understanding polymers’ behavior at the nanoscale level is a subject of continuous research due to the numerous applications of polymer materials in microelectronic devices, solar cells, smart coatings, nanocomposites, and many others.[1−5] The interest in nanoscale phenomena is because when the size available for the polymer chain mobility approaches that of finite length, its dynamic and static properties can drastically change compared to what we usually term a “bulk”
By employing dielectric spectroscopy (DS) and differential scanning calorimetry (DSC), we have investigated the influence of the changes in surface polarity on the segmental dynamics of PMPS 2.5k confined in nanoporous alumina templates with 80 nm pore diameter
To control the surface conditions, we have functionalized alumina oxide (AAO) membranes using highly polar propyl phosphoric units separated by the assumed concentration on nonpolar triethoxysilane groups

Summary

Introduction

Understanding polymers’ behavior at the nanoscale level is a subject of continuous research due to the numerous applications of polymer materials in microelectronic devices, solar cells, smart coatings, nanocomposites, and many others.[1−5] The interest in nanoscale phenomena is because when the size available for the polymer chain mobility approaches that of finite length, its dynamic and static properties can drastically change compared to what we usually term a “bulk”. The surface effects have an enormous impact on the polymer’s dynamics.[9,20−28] Strong attractive interactions can lead to the adsorption of the polymer segments on the surface by forming hydrogen bonds. This produces a gradient in dynamics across the film or nanopores, resulting in more than one glass-transition event in a confined geometry. Those located away from the supported surfaces are weakly or entirely not affected by confinement

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